1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a photodiode for converting optical signals into electrical signals and a method of manufacturing the photodiode.
2. Description of the Related Art
Typically, a photodiode for use with an optical element is an optical senor that produces an electrical signal (e.g., a current or voltage) in response to an optical signal by converting optical energy into electrical energy. A photodiode is a diode in which a junction unit thereof has an optical detection function. A photodiode utilizes the principle that excessive electrons or holes, which are generated by photon absorption, modulate the conductivity of the photodiode. That is, the electric current produced by a photodiode varies according to the generation of carriers in response to incident photons, thus providing a useful method for converting optical signals into electrical signals. In use, a photodiode can function as an interface, which reads and writes data stored in an optical disk or which transmits signals to a servo by converting optical signals into electrical signals.
Examples of photodiodes having an optical detection function include a photodiode having a P-N junction structure, a P type electrode—intrinsic epitaxial layer—N+ type layer—P substrate (PIN) photodiode, an N type electrode—epitaxial layer—P+ type layer—P substrate (NIP) photodiode, and an avalanche photodiode (APD), which uses an avalanche breeding effect. An ‘I’ region of an NIP or PIN photodiode, which can be an intrinsic semiconductor region, has a high resistance, can be composed of a material other than a true intrinsic semiconductor, and controls the width of a depletion region. Such photodiodes are widely used in CD, DVD, DVD RAN, COMBO, COMBI, Blue ray drives, etc.
The performance of a photodiode is evaluated by its photoefficiency and frequency characteristics (e.g., bandwidth). A photodiode can achieve a high performance if it has a high photoelectric efficiency at wavelengths of detected light and a sufficient response speed. Currently, research is under way for improving the performance of photodiodes. For example, in order to improve the photoefficiency of light having a desired wavelength, the reflection of light projected into a light-receiving unit of a photodiode must be prevented. To do this, an anti-reflective coating (ARC) can be formed on the upper surface of a light-receiving unit of a photodiode. The type and thickness of the ARC may be selected by taking into account the wavelength and the amount of light projected into the light-receiving unit. For example, a silicon nitride layer (SiN) or stacked layers of a silicon oxide layer/silicon nitride layer (SiO2/SiN) may be used as the ARC. Examples of semiconductor devices including a photodiode with an SiO2/SiN structured ARC are disclosed in Japanese Patent Publication Nos. 2003-163344 and 2003-110098.
Before an ARC is formed, however, a semiconductor surface of a light-receiving unit of a photodiode is exposed by selectively removing an interlayer insulating layer and an intermetal insulating layer of the light-receiving unit by etching. This process inevitably results in over etching the semiconductor surface because the thicknesses of an interlayer insulating layer and an intermetal insulating layer are not uniform on a semiconductor wafer where the ARC is being formed. This over etching damages the semiconductor surface, thus increasing a leakage current of the photodiode.
FIG. 1 is a sectional view of a conventional NIP photodiode. Referring to FIG. 1, a P type buried layer 102, a P type epitaxial layer 103, an N type epitaxial layer 105, and an N+ type high density doping layer 108 are sequentially formed on a P type semiconductor substrate 101. A P type first junction region 104 and a P type second junction region 106 are respectively formed on the P type epitaxial layer 103 and the N type epitaxial layer 105. Also, a P+ type layer 109b is formed in the P type second junction region 106, and is in contact with a metal contact plug 113a of an anode electrode. A P+ type dividing layer 109a is formed on the N type epitaxial layer 105 to divide a light receiving unit of a photodiode. Metal interconnecting structures 113a, 113b, 115a, and 115b, including an anode electrode, are insulated by an interlayer insulating layer 112 and an intermetal insulating layer 114. A device isolating layer 107 is formed, for example by local oxidation of silicon (LOCOS) to separate a photodiode from neighboring elements. An SiO2 layer 120a and an SiN layer 120b form an ARC 120 for blocking the reflection of projected light on the surface of the photodiode. The NIP photodiode includes a light-receiving unit that functions as a window through which light enters.
FIGS. 2 through 7 are sectional views illustrating a method of manufacturing a conventional NIP photodiode. First, as shown in FIG. 2, a P type high density doping buried layer 102 is formed on a P type semiconductor substrate 101, for example a P type silicon substrate, and a P type epitaxial layer 103 is formed on the P type buried layer 102. Then, a P type first junction region 104 is formed in the P type epitaxial layer 103. Next, an N type epitaxial layer 105 and a P type second junction region 106 are formed on the P type epitaxial layer 103 and P type first junction region 104, respectively. Then, a device isolating layer 107 and an N+ type layer 108 for contacting a cathode are formed on the N type epitaxial layer 105. A P+ type layer 109b for contacting an anode and a P+ type layer 109a for dividing a light receiving unit are formed in the P type second junction region 106.
Next, referring to FIG. 3, an interlayer insulating layer 112 is deposited on the resultant structure and a contact hole 112a exposing the P+ type layer 109b is formed by a photo etching process. Then, referring to FIG. 4, metal is deposited to fill the contact hole 112a. Then, a contact plug 113a and a first metal interconnecting layer 113b are formed by photo etching and an intermetal insulating layer 114 is deposited on the resultant structure. Then, referring to FIG. 5, a via 115a and a second metal interconnecting layer 115b are formed on the intermetal insulating layer 114 and the first metal interconnecting layer 113b. 
Referring to FIG. 6, a photo-resist pattern 150 is then formed on the resultant material to open a light-receiving unit. The semiconductor surface of the light-receiving unit is exposed by selectively etching the interlayer insulating layer 112 and the intermetal insulating layer 114 using the photo-resist pattern 150 as an etching mask. Thus, the N+ type layer 108 and the P+ type layer 109a are exposed in the light-receiving unit. During this process, over-etching the exposed semiconductor surface of the light-receiving unit may occur because the thicknesses of the interlayer insulating layer 112 and the intermetal insulating layer 114 are not uniform over the entire wafer. Thus, when a dry etching is used, the exposed semiconductor surface may be damaged. Finally, as shown in FIG. 7, an ARC 120 including an SiO2 layer 120a and an SiN 120b layer is deposited on the entire surface of the resultant structure.
Therefore because, over etching damages a semiconductor surface the amount of leakage current in a photodiode increases making it difficult for the photodiode to detect an optical signal and thus have high performance characteristics.